The present invention relates to a processing method and a processing apparatus for treating a substrate surface such as that of a semiconductor substrate.
In manufacturing semiconductor devices it is often required to process the substrate surface at high density and high precision, but when the substrate surface is extremely undulated as may result from a series of surface processing steps, it is often extremely difficult to process the surface in subsequent steps. In such a case, a technique which is sometimes employed is that of filling the recesses of the substrate surface with an appropriate material to make the substrate surface flat and smooth.
As an example, FIG. 5 shows a part of the surface of a solid state image sensor. As shown in FIG. 5A, an impurity diffusion region 22, such as a photodetector, is formed in a surface region of a semiconductor substrate 21, and then a transparent insulating film 23 is formed on the surface of the semiconductor substrate 21. Although shown conceptually in FIG. 5, actually, silicon gates and oxide films must be successively stacked up on the protective film 23 between adjacent diffusion regions 22, 22. As a result, a concave part 24 is formed above the diffusion region 22 of the semiconductor substrate 21, while a convex part 25 is formed between adjacent diffusion regions 22, 22.
It is difficult to form a color filter on an undulated surface, such as that shown in FIG. 5A. Accordingly, as shown in FIG. 5B, the concave part 24 is filled with an appropriate transparent material 26 to make the substrate surface smooth and flat.
Later, as shown in FIG. 5C, a color filter 27 is formed on the flattened substrate surface. The color filter 27 is composed by applying materials 30 sequentially. These materials are selectively dyed with organic dye-stuffs on the basis of gelatine, casein or the like within the region sectioned by interlayer 28 and separation layer 29. Subsequently, the surface is covered with protective film 31.
FIG. 6 shows another conventional substrate surface flattening method.
As shown in FIG. 6A, the surface of substrate 32 includes concave parts 33 and convex parts 34. An insulating film (for example, an oxide film) 35 is formed on the surface of the substrate 32.
On the surface of substrate 32, as shown in FIG. 6B, for example, a transparent polymer resin 36 having an approximate viscosity is applied. As a result, concave parts 33 are filled with polymer resin 36a. Polymer resin 36b also builds up on the surface of convex parts 34, however.
If polymer resin 36 is not photosensitive, as shown in FIG. 6C, a photoresist 37 is applied on the surface of the polymer resin 36, and the photoresist 37 is patterned by using a photomask (not shown). As a result, the portion 37b corresponding to the convex portion 34 is removed, and the portion 37a corresponding to the concave portion 33 is left over.
When the substrate surface is then etched, as shown in FIG. 6D, the polymer resin 36b on the convex part 34 is removed, and the concave part 33 is filled with the polymer resin 36a and part 37a of photoresist. Afterwards, by removing the residual photoresist 37a, the substrate surface may be almost flattened. In this state, however, since the polymer resin 36a builds up in the marginal area of the concave part 33, substrate surface is not perfectly flat.
Accordingly, the substrate 32 is heated to about 200.degree. C. Then the viscosity of the polymer resin 36a is lowered, and its fluidity is increased, and by the function of the gravity of the polymer resin 36a moves into the concave part 33. As a result, as shown in FIG. 6E, a smooth flat surface is formed on the substrate surface.
Meanwhile, when a photosensitive material is used for the polymer resin 36, for example, a PMMA photoresist, the photosensitive polymer resin 36 may be directly exposed and developed by using a photomask, without using photoresist 37 as shown in FIG. 6C, so that the state in FIG. 6B may be directly formed into the state in FIG. 6E.
In such prior art, however, it is necessary to remove the material on the convex part 34 by photolithography. In other words, it still requires a photomask to be matched with the undulation pattern on the substrate surface, and this photomask must be aligned with the undulation pattern of the substrate surface to be exposed and developed. Accordingly, due to the photolithography process steps, the number of process steps required is increased and the yield may be reduced because of the risk of photomask defects or photomask shape defects induced by dust or the like.
It is hence a first object of the invention to provide a method for processing a substrate surface in order to form a smooth flat surface on the surface of the substrate to be processed, by filling the concave parts of the substrate surface with a substance, without resort to photolithography.
It is a second object of the invention to provide a processing apparatus for easily executing such substrate surface processing method.